Blaming dice is ignoring all the times when they roll well for you, to instead focus on poor results that will happen due to random variation.
People who like to blame dice should not play games that use dice.
There are some games where your dice just leave you hanging. I was at last year's Regionals vs. a list I felt comfortable with. My dice were just horrid. I've replayed the match many times in my head, but I wouldn't have done anything different. I mean, I had Xizor and 5 Z-95's firing for 4-5 turns at a Decimator and I couldn't even take it down to half health?
With that said, I'm OK with it being the dice. I'm OK that I lost and all that. It still was the dice. It wasn't one critical roll that failed me, which is what a lot of people like to blame on bad luck. I've also played games where my opponent just couldn't catch a break. There have been games I would've lost if my opponent was rolling average dice results.
Bad dice happens, but I just don't get bent out of shape about it. Yes, maybe some people blame bad dice more than they should. There can be other things they could've done that would've changed their outcome, but bad dice rolls do exist in games.